1. Field of the Invention
The present invention generally relates to methods and apparatuses for detecting an edge of a transparent substrate, and processing apparatuses. More particularly, the present invention relates to techniques for detecting an edge of a transparent substrate having optical isotropy, which are used in liquid crystal display (LCD) panels and the like.
2. Description of the Related Art
In manufacturing of LCD panels, it is important to accurately detect an edge of a substrate since various thin films are laminated at predetermined positions on a transparent substrate.
For example, Japanese Published Patent Application No. H03-6406 discloses a method for detecting an edge of a transparent film, in which light from a light source is converted to linearly polarized light by a polarizer, a part of the linearly polarized light is transmitted through a transparent film, the light transmitted through the transparent film and another part of the linearly polarized light are directed to an analyzer for transmitting only linearly polarized light that is perpendicular to the linearly polarized light therethrough, and the edge of the transparent film is detected from the light transmitted through the analyzer.
Incidentally, in LCD panels, flexible display panels using flexible film substrates have been developed instead of conventionally used glass substrates. Film substrates for use in LCD panels are required to have very high optical isotropy in order to accurately transmit linearly polarized light, transmitted through the film substrate, to a liquid crystal layer.
For example, Japanese Published Patent Application No. H07-300559 discloses a solution composition having an aromatic polyethersulfone dissolved in a solvent containing 1,3-dioxolane, and a method for manufacturing a film, in which an aromatic polyethersulfone film having an excellent surface property and excellent optical isotropy is obtained by a casting method by using the solution composition.
Moreover, Japanese Published Patent Application No. 2004-346199 discloses a method for manufacturing an optical film, in which a film is taken up at a take-up speed of a predetermined range when the film is manufactured by extruding a maleimide-olefin copolymer and an acrylonitrile-styrene copolymer by a T-die melt extrusion method, and passing the extruded film on one or a plurality of cooling rolls. Japanese Published Patent Application No. 2004-346199 describes that, since the optical film obtained has excellent optical isotropy, the optical film can be preferably used as a transparent electrode film, a protective film for polarizing films, a retardation film, and the like, which are used in LCD devices and the like.
Incidentally, the edge detection method disclosed in Japanese Published Patent Application No. H03-6406 is a method for detecting an edge of a transparent film by using optical activity (optical rotatory power) of the transparent film. Thus, this edge detection method has a problem that no substrate edge is detected in optically inactive film substrates, for example, film substrates having optical isotropy for use in LCD panels, such as those disclosed in Japanese Published Patent Application No. H07-300559 and Japanese Published Patent Application No. 2004-346199.